The STLE Compass, Released August 23, 2011
“Extending Rolling Element Bearing Life: The Interdependence of Lubrication, Environment and Material” with Dan Snyder

KARA: Hello, I’m Kara Lemar. Welcome to the STLE Compass, brought to you by the Society of Tribologists and Lubrication Engineers. The STLE Compass is your convenient and reliable resource for the latest industry developments.
This is another episode of The STLE Compass and today we’ll take a look at bearings, bearing life, and proper selection for extending that life. Our interviewee has previously written many publications, and on the topic of extending bearing life, we’re going to explore his experience on what works, what doesn’t, and how to get the best operation and life out of your bearing.
Dan Snyder has worked in the bearing industry for 50 years and has seen many changes and improvements that have greatly affected bearing performance. His experience has included design, lubrication, testing, failure analysis and application analysis of rolling bearings. He is a Professional Engineer and a member of STLE and ABMA. He has written many technical articles and has been active in bearing standards.
Dan, welcome to STLE Compass.
DAN: Thank you.
KARA: You’ve been in the field for about 50 years and have had extensive experience working with bearings. Given this experience, and the topic for today’s discussion (bearing life), what opening comments do you have?
DAN: Well it’s kind of interesting being in bearings for so long, and you run into people and you tell them you’ve been in bearings that long, they think, oh what a boring field – bearings. But it’s been very exciting. There are a lot of changes that have been happening in materials and tools, manufacturing the tools, calculating design – it’s very exciting and hasn’t been boring at all. So I think people who are accustomed to using bearings probably think, well they take them for granted, but there has been a lot of technology that’s come down the road the last 5-10 years and people may not be aware of are not taking advantage of it when they could.
KARA: Okay. And, in relation to bearing life – what comments do you have about that?
DAN: I think having worked in the industry so long, I think the design of bearings and the manufacturing of bearings has maybe exceeded in some ways the ability of a customer to use it. If you get into the high tech industries – aerospace, in some cases automotive, they are getting the maximum out of their bearings for the design. But I think in most industrial applications the designs that are being made today and put in the marketplace are probably exceeding in most applications what is happening. I think that the customer the way they are installing them, the way they are maintaining them, and the way they understand how to use the bearings is killing the bearing before the potential life is being achieved.
KARA: You’re referring to rolling bearings, correct?
DAN: Yes. Rolling bearings. And I think it’s probably somewhat true in plain bearings, but I’m particularly talking about rolling element bearings today.
KARA: So, what are the different types of bearings and how do you distinguish between them?
DAN: Well, there is what we call the sliding bearing or just like a bearing with a lot of friction, maybe a hydrodynamic bearing, a sleeve bearing, or something of that nature as opposed to one that has balls or rolls in between the inner and outer ring which helps reduce the friction and gives you less friction during rotation, gives you higher load carrying capability in a smaller envelope.
KARA: In the last few years, there has been a lot of debate around ISO 281:2007. What are your thoughts on it?
DAN: Well, I think there is a lot of misunderstanding around it. ISO 281:2007 is a further attempt to better calculate ahead of time what the life of bearings is going to be in the design phase and also to better calculate what the effects of the environment are on the bearing life. So, to do that, it means you have to know more about the application and sometimes if you oversimplify it, then all of a sudden you’re not taking advantage of everything that’s being offered in ISO 281:2007. I think the old standards, I call them standards (ISO or ABMA standards) have been around for awhile and it’s been recently – and it goes back to what I was saying before about bearing life, the designs and manufacturing exceeding what most people will see – but I think these calculation methods now, in 2007, I think they’re trying to find a way to come up with a calculation method which matches the life that you would actually see in, say, a clean environment or a laboratory type environment, and that’s what’s been done. It’s also a way of trying to account for things like contamination, lubrication, things that in an application will cause a bearing to fail before it’s intended to. So the standard is including some of those things in it now, which is new.
KARA: Okay, and it hasn’t actually been passed or accepted in the U.S., so what would be needed to get it to that point and what happened there?
DAN: Yes, it hasn’t been accepted as a standard. It’s being used because a lot of manufacturing or bearing companies in the U.S. are international. So, there are companies from Japan, companies from Europe, and so on that are using this standard. Some companies here in the U.S. are using those standards because they interface very closely with those. There’s another group of customers that buy bearings and do their own design and maybe aren’t in tune with the latest technologies or maybe they don’t have a good handle on their actual application conditions to be able to use the standard. So there tends to be a fallback into the old standards that date back into the early 1990s. One of the things you have to watch out for is, when people write specifications, whether it be an OEM or end user, they may refer to a standard. So if there’s a standard referred to, it’s hard for a supplier to just go back and change the way of calculating because now the specifications they’re supplying to have not been changed. It’s almost like they change an oil specification, maybe someone in automotive is buying a gear oil and they were referencing some SAE specification, well now, if you start testing the oil to a different specification and doing some calculations based on new specifications, the user may not accept that because they are still referring to the old specification. So, I think there’s a lot of education that has to go along with ISO 281:2007. ISO 281:2007 has been developed and formulated by people who are very close to bearings. Now, the people who aren’t so close to it are the ones that actually have to use it, so I think the people who developed this have to do a little better job of informing and training people on the attributes of it, and where you can use it, not use it, and what’s required to use it.
KARA: Education is probably a step in the right direction, but as far as getting it passed…?
DAN: Well, that’s part of it because in order to get it passed, it has to go through ANSI, the American National Standards institute here. The bearings are looked after within ANSI by ABMA (American Bearing Manufacturers Association), so ABMA is responsible for the bearing standards within the United States. So, there is a committee within ABMA that’s responsible for looking after the standards in the U.S. for bearings. That committee is the one that hasn’t fully accepted it yet. Now, that committee is made up of people who maybe have been in the industry a long time, maybe consultants, maybe people who are casual users to bearings, maybe people who have a vested interest and have a lot of experience with the old standards, that maybe they haven’t had the experience and were not part of the development of the new ISO 281:2007. So those people say, well, I don’t know if I really believe this because I haven’t seen the data, and that’s a fair judgment, because maybe they haven’t. And that’s why I think we need to do a better job of, if people have questions – let’s be sure that we have some conversation with the people who are rejecting the standard. It’s a little like the budget debate. Everyone has a different opinion. So, it’s a matter of getting everything on the table – and say, okay, what do we know, what don’t we know, what works and what doesn’t work? Unfortunately, there have been a lot of countries within ISO that have done this, but it hasn’t happened to a very large extent in the United States.
KARA: Okay, so just some education and communication between the two different parties?
DAN: Yes. And I’ll say one thing, too, Kara. Back in the 1960s, ABMA and the U.S. used to be a leader in bearing technology and bearing standards. At that time, a lot of the test work was being done, or sponsored by the U.S. government, whether it be the Air Force, the Navy, the Space Program, jet engines, etc., that was work that individual companies were doing, government-sponsored, but then, when the work was over, the test data became public knowledge. Then it was very easy to take that data and go back and develop standards and do something with it. Well, we all know what’s happened with some of those programs, and now there is less funding from the government. A lot of those companies are doing the same research, but they’re not sharing it among each other, or with the public. So, there’s data there, but it’s more in pockets and it’s not generally known the way it was back in the 1960s and 1970s, when some of the original standards were developed.
KARA: So, that bank of information isn’t available to everyone, and that might have resulted in the two different opinions. If some people know and have the data, then they can argue for it, but others might not have access. That would create a rift.
DAN: Exactly. When the ISO 281:2007 was developed, there were experts and these experts were from different bearing companies that had the data. So, there are formulations put forward, and they’d all go back with that formulation and crank it through their data to see if their data would fit with it. They’d come back and say, well we don’t fit here, so we have to tweak it here and the other company would say, yes, I can live with that, and we end up with something like 281. Unfortunately, the people in the U.S. were not part of that committee and did not share in all that development or exchange of information.
KARA: So that would put a hitch in things.
DAN: Yes.
KARA: Now, you’ve had a lot of experience and you’ve written some articles and you mentioned it briefly, but you said that bearing life is interdependent upon three different components: lubrication, environment, and material. Can you talk about that? Is there an important one; is one more important than the others?
DAN: No, I think they’re all equally important. I’ll give you a good example. You can take a bearing and make it to the highest precision you want to, and put it into a jet engine and run it for an extremely long period of time. If you take that same bearing and put it in a steel mill that doesn’t use any filters in the oil, uses a poor grade of oil and it’s a very dirty environment, that bearing won’t last. So what happens is, no matter what kind of material you use, no matter what kind of precision you put into that bearing, it was killed by how it was used, or how it was installed. For instance, if someone installed it with a sledge hammer and created some indentations on it, as opposed to properly installing it. The other thing is too, you could have someone who is not paying attention to how they are using the bearing. The bearing was put into a piece of equipment originally, and that piece of equipment is 20 years old, and then the decision is made to increase production on that equipment. So you increase the speed, or maybe you change the lubricant, and now the bearing that was running successfully for all those years, is suddenly failing, and it may be due to increased temperatures because someone increased the speed, put a bigger motor on it, maybe the weight or volume of material that you’re running through that machine is increased, that’s all putting stress on the bearing that really wasn’t intended. That’s what I mean by environment, controlling the environment includes the temperature, speed, and lubricant. And then not fooling around with synthetics, or different additive packages. All those can have an influence, and they all interact with each other. You can’t say that I’ll put this material in and I’m going to get two times better life. You may under one set of conditions, but it may not have any effect under a different set of conditions. So, that’s why it’s all interdependent.
KARA: Yes. It’s an aggregate. This and this and this all work together, and you have to plan for how you’re going to use it.
DAN: If I could go back, because that brings up a good point about the ISO 281:2007 and the ABMA Standards 911. Back in 1990, the way that environmental conditions were treated in bearing life calculations were factors. You’d have a factor let’s say for temperature, a factor for lubrication condition, etc. and then you’d have a multiplication for these factors to come up with an adjusted life. The way the ISO 281:2007 works is looking at the interactions. No matter what all these factors are, all those will create stress on a material. So the ISO 281:2007 is based upon the stress in the material caused by all those factors in saying the life of the bearing, the life of the material is a relationship between the stress created by those things and the type of material you have, and that determines the life, as opposed to the factorial approach. So that was the big change between ISO 281:2007 and the old approach. So, some of the people who have been using a lot of factors through the years are maybe struggling giving up those factors and going back to a different way of calculating.
KARA: Certainly. And you mentioned bearing life adjustment in an article you wrote for TLT (Tribology & Lubrication Technology), “Selecting Rolling Element Bearings for Modern Applications.” Can you talk about the different factors that you covered in the article?
DAN: Sure. If you’re developing a bearing for a brand new application, and you’re going to have your customer come to you and say, “I want a bearing that will last so long, it’s going to have this load, and it’s going to run at this speed and at this temperature.” Well, if the machine has never been built, they really don’t know what the temperatures are going to be. They don’t know how the user is going to use it. And so, when you design that bearing, you’re taking that set of conditions that’s been defined to you up front and selected a bearing and a size that’s going to meet the requirements that have been specified. So if you change the temperature by just ten degrees Fahrenheit, which changes the viscosity, or if you use a different type of oil, of all of a sudden, the machine or shaft size is bigger than what they thought originally because they designed something different, and now the load on the bearing is ten to fifteen percent higher. That means the life of the bearing in the application is going to be totally different than when it was designed because those conditions are not reached. So, no one goes back to the design criteria and looks to see what happened there. They may say the bearing is undersized, or whatever. Well, maybe so for the conditions you ended up with, but those may have not been the set of conditions that were used initially to size the bearing.
KARA: So they would need to keep revisiting it as they go and make sure that every component, every bearing is up to speed and in the right condition.
DAN: I think it also points out that you don’t do anything in a vacuum today. If you’re a manufacturer of anything and you have a customer, you have to know how that customer’s customer is using the product. And so your customer has to have a good understanding of how their customer is using the product and those three have to talk to each other and be aware of what is happening in that application and that’s where you get the good designs. You can’t have someone designing something or specifying something for a wind turbine, paper mill or steel mill and then going back and specifying to an electric motor manufacturer, to a pump manufacturer – just give me this pump, without having some link because I think the same thing is true – we have to be aware of the total environment and work together to do that. And that’s something new. We’re not used to doing something like that.
KARA: So, what are some examples that you’ve seen of maybe an incorrect set up or things that have gone wrong when people haven’t planned correctly?
DAN: Well, maybe not considering cleanliness. We know today that clean oil is very important and so if you assume that the oil is going to be clean, but it goes into an application and maybe it’s a dirty environment, it’s going to be used in a mine as opposed to being used in a paper mill. The same electric motor, the same pump, the same gearbox, if it’s used outdoors in a mine, it’s going to have totally different conditions. And so, we have to have a little bit better understanding. And I think people are starting to ask questions about that now. You’ve seen a lot of labs that have popped up in the last years of looking at oil analysis and of course, even within STLE, there’s a lot of work being done around condition monitoring, and being able to control those conditions. Likewise, on the vibration side, there has been a lot of work done on monitoring the vibration of the equipment, to be able to use the vibration to detect things like misalignment, things like out around, to see the bearing property to begin with. So, this all ties together to be sure your operating conditions are ideal for the bearing and for the machine.
KARA: What would you say someone should take away from today’s discussion? What do you want them to know? What advice do you want to relay?
DAN: Well I think if you have a bearing, you have to think a bearing is not a bearing, is not a bearing. All bearings are not created equal. There are differences in designs. So, if you have an application, and let’s take first if you’re the MRO side, the end user: if you have an application where something started to happen and it worked fine for a long time and all of a sudden a bearing failed, you replaced it and it failed again, and then you think, something is wrong with this bearing. Well, probably not. You have to be very careful that maybe something changed in your environment, in your conditions that you weren’t aware of. And so I think the key for that end user: get the OEM involved or get the bearing supplier involved and work on it together, because you certainly don’t want to start changing bearings or start changing other things, trying to correct it yourself because there are other technologies and other knowledge out there that you might not be aware of that these other people have that maybe could help you solve that problem a lot simpler. If you’re an OEM, then I think you need to be a little bit more aware when you put specifications on a bearing supplier. Be more aware of what things in the application can kill the bearing and what’s the effect of the different things in the application. So work with your bearing supplier and have a discussion around how the bearing is actually going to be used, how the piece of equipment is going to be used and what you want out of the equipment that the bearing is going into. Are you trying to produce an expensive piece of equipment? Are you trying to get a long-life piece of equipment? Do you want to have a high value in the marketplace? What are you trying to do? The bearing supplier can work with you on that. I think there needs to be a discussion. The last thing you want to do is buy a bearing off the shelf because when you do that, you tend to think that all bearings are created equal, you treat them like a commodity, and that’s not true.
KARA: Thank you Dan for joining us today and for your insight.
DAN: You’re quite welcome.
KARA: I’m Kara Lemar. For more news, information and research on extending bearing life, you can visit our website. Thank you for joining us today. This has been another episode of The STLE Compass, pointing you in the right direction.

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